(a) Field of the Invention
This invention relates to a zoom lens system, especially a zoom lens system employing a new focusing method.
(b) Description of the Prior Art
The most general focusing method of a zoom lens system is the one in which a zoom lens system has a focusing lens group which is fixed at the time of zooming, and focusing is done by having this lens group moved only at the time of focusing.
A known focusing method of this kind has a defect that the diameter of a front lens inevitably becomes large because the front lens is moved towards the object at the time of focusing.
In order to overcome the above mentioned defect, one may consider a focusing method in which focusing is done by moving at least one of lenses in the movable lens groups which is moved at the time of zooming. In this focusing method, the above mentioned lens which is moved for focusing has to be moved also at the time of zooming. Therefore, there is a defect in that the movement of the lenses becomes intricate, so that the moving mechanism for the lenses becomes complex.
As the prior art intended to overcome this defect, the zoom lens systems disclosed in Japanese published Unexamined patent application Nos. 29215/84, 31922/84 and 31923/84 are known. In the arrangement shown in each of these prior art references, only a reduction in the amount of movement of the lenses is made and the defect is not overcome completely.